Referring to FIG. 1, FIG. 1 illustrates a cross-sectional view of a conventional light emitting diode. The light emitting diode comprises a substrate 100, a n-type semiconductor buffer layer 102, a n-type semiconductor contact layer 104, a n-type semiconductor cladding layer 106, an active layer 108, a p-type semiconductor cladding layer 110 and a p-type semiconductor contact layer 112 stacked in sequence. The light emitting diode further comprises a p-type contact pad 114 located on a portion of the p-type semiconductor contact layer 112, and a n-type contact pad 116 located on the exposed portion of the n-type semiconductor contact layer 104.
The material of the substrate 100 of a conventional light emitting diode adopts n-type gallium arsenide (GaAs). The substrate 100 composed of n-type GaAs can absorb light, so that most of the photons produced by the active layer 108 of the light emitting diode while emitting toward the substrate 100 are absorbed by the substrate 100, thus seriously affecting the light emitting efficiency of the light emitting diode device.
In order to avoid the issue of light absorbed by the substrate, I. Pollentirer et al. in the Gent university in Belgium disclosed a technology in the journal “Electronics Letters” about directly bonding the GaAs light emitting diode wafer to the silicon (Si) substrate after the GaAs light emitting diode wafer is stripped off the GaAs substrate in 1990. Additionally, the U.S. Pat. No. 5,376,580 (application date: Mar. 19, 1993) filed by Hewlett-Packard Co., U.S.A. disclosed a technology about directly bonding the AlGaAs light emitting diode wafer to the other substrate after the AlGaAs light emitting diode wafer is stripped off the GaAs substrate. However, the U.S. Pat. No. 5,376,580 has a disadvantage of low yield caused by the need of considering the consistency of the lattice direction between the bonding wafers. Furthermore, the U.S. Pat. No. 6,258,699 (application date: May 10, 1999) filed by K. H. Chang et al., Visual Photonics Epitaxy Co., R.O.C. disclosed a technology about using metal as a bonding agent after the light emitting diode wafer is stripped off the growth substrate. However, a disadvantage of the U.S. Pat. No. 6,258,699 is that: the light emitting diode wafer is easy to peel off after bonding, thus lowering the yield.